1. Technical Field
The present invention relates to a discharge amount evaluation method of a liquid droplet discharging device.
2. Related Art
In the recent years, much attention has been paid on film forming techniques using a liquid droplet discharging method. The liquid droplet discharging method allows a minute liquid including a film forming material to be placed in intended positions to form a minute film pattern. Thereby, patterning can be achieved more easily than in photolithography, and wasted use of the film forming material can be reduced, resulting in saving of production cost.
The liquid droplet discharging method uses a liquid droplet discharging head. For example, the liquid droplet discharging head includes a large number of discharging units placed in an X direction. Each of the discharging units includes a liquid reserving section, a nozzle, and a piezoelectric element pressurizing a liquid to push it out from the nozzle. The liquid droplet discharging head scans over a film forming surface in a Y direction to discharge the liquid from the discharging units so as to place the film forming material on the surface.
For the liquid droplet discharging head, it is necessary to discharge an equal amount of the liquid from the discharging units. If the amount of the liquid discharged varies, a film thickness in the Y direction also varies. For example, in production of a color filter for an image display apparatus or the like by the liquid droplet discharging method, a film thickness variation on the color film may be recognized as a streak along a scanning direction (a streak variation), leading to deterioration of display quality.
In order to reduce such discharge amount variation, for example, JP-A-2003-159787 discloses a technique for controlling a discharge amount of each discharging unit. The technique reduces the discharge amount variation by controlling discharging operation of discharging units that discharge an amount of a liquid droplet significantly different from a predetermined value. For application of the technique, it is extremely important to accurately know a discharge amount per discharging unit, since control of the discharge amount can be suitably accomplished by knowing a difference between the discharge amount per discharging unit and the predetermined value.
Among discharge amount evaluation methods, there is a known method for calculating a volume of a shape of a liquid discharged. In this method, first, the liquid is placed (discharged) on a testing substrate by a liquid droplet discharging head. Then, by evaporation of a liquid component included in the placed liquid, such as a solvent or a dispersion medium, there is obtained a solid made of a solid component in the liquid. Next, using an optical interference method or the like, an outline of the solid is measured on a measurement plane parallel to the testing substrate. The outline measurement is performed on a plurality of measurement planes obtained by changing a distance between the testing substrate and the measurement plane.
On each of the measurement planes, an area surrounded by the outline of the solid is calculated to obtain a cross-sectional area of the solid on the each measurement plane. Thereby, there can be obtained a cross-sectional area of the solid with respect to a distance from a bottom to a top (a height) of the solid, and then, the obtained cross-sectional area is integrated by the height to obtain a volume of the solid. Since a composition of the liquid discharged is known, a volume of the liquid can be reversely calculated from the volume of the solid, so that the discharge amount can be evaluated.
However, the above evaluation method cannot evaluate the discharge amount with high precision and high efficiency because of following reasons.
In the evaluation method, the outline measurement is performed after drying the liquid. For example, if the method requires a drying time of approximately eight hours, efficient measurement is impossible. In order to reduce the drying time, heating processing or the like may be considered. However, such processing may cause, for example, an increase of an additional step and reduction in evaluation precision due to deterioration or the like in quality of the liquid caused by heating.
Furthermore, in order to improve the evaluation precision of the evaluation method, it is conceivable to increase measurement precision of a three-dimensional shape of the solid. For example, multiple-point measurements can be performed by variously changing the distance between the testing substrate and the measurement plane. In this case, however, in each measurement, an optical interferometer needs to be adjusted for each measurement plane to pickup an image of the solid. As a result, it takes a large amount of work and time to perform the multiple-point measurements, thereby making the measurements inefficient.